Variable-bit-rate (VBR) encoding refers to a video encoder's ability to vary an amount of data used to encode a scene based on an overall complexity of information being encoded. A video scene with a large amount of detail and movement, for example, may be encoded using more data than a scene that is relatively simple and lacks motion.
Pre-encoding refers to encoding an entire video before the video is delivered. Pre-encoding may involve an encoder analyzing the entire video to be encoded to generate a more sophisticated encoding. When encoding a movie, for example, the entire movie can be analyzed to determine which parts of the movie are relatively complex and which parts are relatively simple. The encoder can pre-allocate, from an overall data budget, a specific amount of data for each section of the movie. Such an approach allows the encoder to maintain a limit on the overall size of an output file while optimizing the allocation of data to specific parts of the movie. Video quality can be optimized within the constraint of an overall file size.
The combination of VBR and pre-encoding enables higher-quality video (when compared to other encoding mechanisms) to be delivered using the same amount of data. Pre-encoded VBR content is a common type of encoded content for many download-to-play video services found on the Internet. Encoding schemes and/or video distribution and display systems are evaluated using video quality and acceptability test procedures. These procedures often involve multiple pieces of video content to provide a diverse set over which to test.